As shown in FIG. 5, a phosphor screen (not shown) is formed on the front inner wall 4 of the glass panel 1 of a cathode ray tube by three kinds, red, blue and green, of phosphor matrices to reproduce the three colors. In addition, a black matrix film 7 is formed on the front inner wall 4 by filling the space among the phosphor matrices with a non-luminescent black substance such as graphite. The black matrix film 7 provides a margin for beam landing and is intended to improve contrast.
In general, the black matrix film 7 is formed by coating the inner surface of the glass panel 1 with a photosensitive material, exposing and developing the photosensitive material properly to form the desired photosensitive pattern, coating the inner surface of the glass panel 1 with a graphite slurry, which is a black substance, and removing the photosensitive pattern with a reverse liquid.
In this method for forming the black matrix film 7, the excess black substance coating film is peeled and removed by the reverse operation after coating the inner surface of the glass panel 1 with the black substance and drying the black substance. Therefore, the black substance coating film adhered to the skirt inner wall 5 and the sealing surface 6 of a skirt portion 3, which are regions where the photosensitive material is washed away and is not adhered, unavoidably remains in the inner surface of the glass panel 1.
Accordingly, the following methods have conventionally been employed to remove such an excess black substance coating film. The excess black substance coating film is cleaned and removed by immersing the skirt inner wall 5 and the sealing surface 6 in hot water, to which ultrasonic vibration is applied, and pouring hot water onto the inner surface of the glass panel 1 at the same time, without using a glass dissolving liquid, such as hydrogen fluoride or ammonium fluoride (see Japanese Laid-Open Publication (Tokkai Hei) No. 5-28916). Furthermore, as shown in FIG. 7, a black substance coating film 8 that is adhered to the skirt inner wall 5 and the sealing surface 6 is removed by washing the black substance coating film 8 away with water 72 using a water-pouring machine 71, while rotating the glass panel 1 in a wet state before the black substance coating film dries.
In addition, Japanese Laid-Open Publication (Tokkai Hei) No. 6-150822 and Japanese Laid-Open Publication (Tokkai Hei) No. 8-17350 disclose methods for removing dirt adhered to the inner surface of the glass panel and a phosphor slurry adhered to the inner surface of the skirt portion by injecting high-pressure water from a nozzle to the inner surface of the glass panel.
With the removing method involving ultrasonic vibration, however, it is very difficult to completely clean and remove the excess black substance coating film once the black substance coating film is dried because a glass dissolving liquid, such as hydrogen fluoride, is not used.
Furthermore, with the removing method using water pouring, it is impossible to perform sufficient cleaning unless a strong water flow is used because the black substance coating film in a wet state is cleaned only with a strong water flow. If such a strong water flow is discharged, water splashes from the discharge opening of the water-pouring machine, contaminating the front inner wall of the glass panel. Therefore, the formation of the black matrix film can be adversely affected.
As described above, with the conventional removing methods, it is not easy to sufficiently clean and remove the excess black substance coating film. Furthermore, when trying to completely clean and remove the excess black substance coating film, a long time is required for cleaning, and water splashing damages the black matrix film.